Plato’s Notion of Justice in the Republic and its relation to Thrasymachus’ Formula that “Justice is nothing other than the interest of the stronger”.

Plato is generally taken to set out his notion of justice in Book IV of the Republic. Unfortunately, though, this has attracted much negative commentary for its apparently immoralist stance and the weakness of the arguments on which it is based. This has in turn led to its being widely discounted as a serious basis for conceptions of justice, and has damaged Plato’s reputation more generally. I claim, however, that the almost exclusive focus on Book IV’s picture is mistaken and that if Book I, and in particular the dialogue between Plato and Thrasymachus, is properly considered it will be seen to offer a significantly improved account of justice. In Book I Thrasymachus defines justice as “that which is in the interest of the stronger”, but this simple formula requires some sophisticated unpacking to be fully appreciated. I argue that establishing four key elements is necessary to its proper understanding. Firstly, rather than depicting four separate objects that correspond to the four cognitive levels, the Divided Line represents a single object (the Form) that is viewed with increasing clarity and sophistication as the subject ascends through the cognitive levels. Secondly, the dialogue between Socrates and Thrasymachus is conducted at the very top of cognitive level III, and, thirdly, that the two key terms for strength and interest respectively, kreisson and sumpheron, are carefully chosen by Plato, and that it is through proper analysis of these specific terms that their full meaning can be ascertained. Fourthly, I argue that Thrasymachus identifies two principles which introduce a crucial distinction between the intrinsic and the instrumental. The resultant self-sustaining notion of Justice within an operating society vindicates Thrasymachus and validates the formula. This, in turn, rehabilitates Plato’s reputation amongst his critics and offers a number of potentially productive avenues of further research based on these findings